19 July 2016

1 | P a g e

Trend and Seasonal Analysis for Dwelling Fire Totals in Scotland over the

seven-year period April 2009 to March 2016

Stewart Ross, Performance Data Services Manager, Scottish Fire and Rescue Service

July 2016

Summary

Over the past seven years there have been declines in Accidental Dwelling fires, but from about mid-

2013 onwards that decline has slowed and to some extent reversed. Deliberate dwelling fires show a

much-steeper decline over the same period, but with a similar tailing off of the reduction since mid-

2013.

Accidental Dwelling Fires peak around December each year and are in general at their lowest in the

summer and early autumn months from June to September.

On average the number of accidental dwelling fires in December is 16% higher than the overall mean

monthly total. In summer the number of accidental dwelling fires is about 7% lower than the overall

mean monthly total.

Whilst there are distinct seasonal peaks and troughs in the occurrence of accidental dwelling fires,

deliberate dwelling fires show an entirely different pattern. Accidental dwelling fires peak in winter and

are at their lowest in summer each year. For deliberate dwelling fires, the median of the winter period

totals is lower than the for the other three seasons.

Seasonal variations in accidental dwelling fires do not have a direct or simple relationship to the

number of fatalities which result. If the likelihood of an accidental dwelling fire resulting in fatalities is

equally spread throughout the year we would expect to see the same pattern in the totals for

accidental dwelling fire fatalities by month, but we do not.

Whilst accidental dwelling fires peak in December and are at their lowest in the summer months, the

number of fatalities per incident is consistently a little lower than would be expected in December and

higher than would be expected in summer if fatality rates were constant throughout all months.

There are clearly other factors than seasonality involved in variations between the number of

accidental dwelling fires and the number of fire fatalities which result from those fires. In due course

we need to take these into account, by modelling for example the type and severity of the incident, and

the causal factors that resulted in a fatality.

19 July 2016

2 | P a g e

Table of Contents

Overall Trends ............................................................................................................................................... 3

Seasonal Monthly Variations in Dwelling Fires ............................................................................................. 6

Accidental Dwelling Fires ........................................................................................................................... 6

Deliberate Dwelling Fires ........................................................................................................................... 8

Accidental Dwelling Fire Fatalities ............................................................................................................... 10

Previous studies ....................................................................................................................................... 13

Appendix 1: Tabulated Statistics ................................................................................................................. 14

Appendix 2: List of Charts and Tables ......................................................................................................... 16

Charts ....................................................................................................................................................... 16

Tables ....................................................................................................................................................... 16

19 July 2016

3 | P a g e

Overall Trends Over the past seven years there have been declines in Accidental Dwelling fires, but from about mid-2013

onwards that decline has slowed and to some extent reversed:

Figure 1: Monthly totals for accidental dwelling fires

The considerable month-to-month variability shown in Figure 1 above is typical of semi-random events with

trend and seasonal components. Using specialist software these can be separated to show the trend,

seasonal and random components involved:

Figure 2: Accidental dwelling fire seasonal decomposition

The de-seasonalised trend line in Figure 2 shows some cyclic variability, with a cyclic upturn around mid-

2013 onwards to the end of the 2014-15 financial year.

Deliberate dwelling fires show a much-steeper decline over the same period, tailing off over the past

eighteen months.

19 July 2016

4 | P a g e

Figure 3: Monthly totals for deliberate dwelling fires

The de-seasonalised trend line for deliberate dwelling fires is more linear but still shows some evidence of

cyclic variability, with a flattening of the trend from mid-2013 onwards:

Figure 4: Deliberate dwelling fire seasonal decomposition

Working with data where there is such seasonal variability one could ask whether the increases in

accidental dwelling fires in particular indicated by the trend lines could be accounted for in some way by

changes in seasonality for instance, as recent winters have been both warmer and wetter than average. In

answer to this we have also modelled the monthly totals for accidental dwelling fires as simple heat-maps,

where the darker cells show larger totals:

19 July 2016

5 | P a g e

Figure 5: Accidental dwelling fires Heat-map

Figure 6: Deliberate dwelling fires Heat-map

The brighter colours of the accidental dwelling fire heat-map cells for January to March 2013-14 show the

unusually-low totals for dwelling fires over that period, with February standing out (the lightest cell on the

lower right of both charts). This coincides with the severe wet weather that winter, though it is difficult to

envisage any form of link between exceptionally wet weather and reductions in dwelling fires. There are

no similar patterns noted for the period of exceptionally wet weather that occurred in late 2015.

19 July 2016

6 | P a g e

Seasonal Monthly Variations in Dwelling Fires To some extent self-evidently fires in the home occur more frequently in the colder weather in winter than

in the warmer summer months. There are distinct seasonal peaks and troughs in the occurrence of

accidental dwelling fires, but deliberate dwelling fires follow an entirely different pattern.

Accidental Dwelling Fires

Accidental Dwelling Fires peak around December each year and are in general at their lowest in the

summer and early autumn months of June to September, though there are some exceptional years as

shown by the lower outlier dots on Figure 7 below

Figure 7: Accidental dwelling fires boxplot

In the accidental dwelling fires boxplot1 above, the totals for June, August, September and December test

as being significantly different to the mean value (within the 1% range for June, September and December,

and the 5% range for August).

The month range values show interesting variability, with ADF totals for July varying much more widely

than the two months on either side. ADF totals in January also show considerable variability, much more so

than in the peak month of December.

Although median and mean values are different measures of central tendency, the mean and median

values for accidental dwelling fires are very closely related and accordingly can be compared almost

interchangeably. The December median value of 488 accidental dwelling fires is 66 above the overall mean

monthly value of 422 ADFs per month, an increase of 16% on the monthly average.

The months with the minimum median values (June and August) are 7% below the monthly average for the

period.

1 Boxplots show the range and variability of the totals for each month. The vertical lines outside the boxes indicate normal

maximum and minimum ranges, with dots representing outlier values. The shoulders of the boxes indicate the 25th and 75th percentile ranges, and the horizontal line within the box indicates the median value (the 50th percentile or middle value, which has been annotated on the chart above for clarity). The mean monthly total for the period 2009-04 to 2016-03 is shown by the dashed line on the chart.

19 July 2016

7 | P a g e

A four-season view of the data shows that accidental dwelling fire totals in general peak in the winter

months each year (December to February) and are at their lowest in summer (June to August), though the

range of dwelling fire totals in winter each year is very wide.

Figure 8: Seasonal boxplot of accidental dwelling fire totals

The summer month mean value tests as being significantly lower than the overall seasonal mean value of

1263 at the 5% level. The summer median, 1168, is 7.5% lower than the overall mean value of 1263

accidental dwelling fires per season.

19 July 2016

8 | P a g e

Deliberate Dwelling Fires

Deliberate dwelling fires are those judged to have been started as a result of a deliberate or wanton act.

Whatever the motivations of the person or persons concerned, the pattern of deliberate dwelling fires

shows none of the seasonal factors associated with accidental dwelling fires.

Figure 9: Deliberate dwelling fires boxplot

None of the monthly means for deliberate dwelling fires are significantly different to the overall monthly

mean of 72 per month, though the month of November shows the widest overall variation and the highest

overall maximum value.

A four-season view of the data shows that unlike accidental dwelling fire totals, those for deliberate

dwelling fires do not peak in the winter months at all. The median for the winter period is lower than the

medians for the other seasons, though none of the means are significantly different to the overall seasonal

mean of 212.

Figure 10: Seasonal boxplot for deliberate dwelling fires

19 July 2016

9 | P a g e

Taking the individual monthly totals for deliberate dwelling fires and plotting these as a bar chart by month

and year shows diminishing differences from the mean value in recent years, with a peak reduction in

February in many years:

Figure 11: Differences between annual monthly mean and individual monthly totals for deliberate dwelling fires

This suggests that the number of deliberate dwelling fires is tending towards a floor value of some kind

which is not varying strongly from month to month at present, give or take random fluctuations.

19 July 2016

10 | P a g e

Accidental Dwelling Fire Fatalities In this section we show that the seasonal variations in accidental dwelling fires noted previously do not

have a direct or simple relationship with the number of fatalities which result.

The monthly totals for accidental dwelling fire fatalities from April 2009 to March 2016 are shown below:

Figure 12: Accidental dwelling fire fatalities by month

If we assume for the moment that increases or decreases in the number of incidents results in increases or

decreases in fatalities the trend line in the Figure 11 may only be showing us changes associated with the

number of accidental dwelling fires, which we know have increasedfrom mid-2013 onwards. We can

instead show the rate of accidental dwelling fire fatalities per thousand accidental dwelling fire incidents:

The increase in fatalities is shown more starkly on the trend component of the seasonal decomposition plot

below:

Figure 13: Seasonal decomposition of accidental dwelling fire fatalities per thousand incidents

19 July 2016

11 | P a g e

We noted earlier that accidental dwelling fires peak in December and are at their lowest in the summer

months. If the likelihood of an accidental dwelling fire resulting in fatalities is equally spread throughout the

year we would expect to see the same pattern in the totals for accidental dwelling fire fatalities by month,

but we do not:

Figure 14: Accidental dwelling fire fatalities boxplot

Further evidence that there are unexpected seasonal differences in the number of fatalities against the

number of dwelling fires can be obtained by plotting the normalised rate of fire fatalities per month

(fatalities divided by the monthly total of ADFs). This shows that whilst fire fatalities peak in Winter they do

not peak in December in most years, despite that month having the largest peak for dwelling fires each

year.

Figure 15: Normalised fire fatality rates per month

19 July 2016

12 | P a g e

Figure 16 above shows that the rate of dwelling fire fatalities is in most cases lower in December than the

other winter months, and very little different to the rate for June each year. This runs counter to

expectations, particularly in light of the average 17% increase in the rate of accidental dwelling fires in the

month of December and the average 7% reduction in the summer months mentioned earlier.

One potential explanation for this phenomenon which requires further research to prove or disprove

would be that the seasonal differences in accidental dwelling fire patterns may be associated for the most

part with the less-severe types of accidental dwelling fire, not the relatively small proportion of fires which

result in loss of life.

Previous work undertaken by SFRS in testing the Cheshire model of fire severity against the Fife model

developed locally by WM Ron Nairn showed that only around 6% of all accidental dwelling fires fall into the

most serious categories of fire severity.

A four-season view of the number of accidental dwelling fire fatalities per thousand incidents shows a peak

in the winter season, but the range is very wide and none of the season boxplots test as significantly

different to the mean value of 21 fatalities per thousand incidents per season.

Figure 16: Seasonal accidental dwelling fire fatalities per thousand incidents

19 July 2016

13 | P a g e

Previous studies

There appear to be very few previous studies published on dwelling fires patterns and seasonality. An older

study conducted by London Fire Brigade in 20032 states that “unintentional dwelling fire deaths follows a

periodic cycle over the course of the year, with more than three times the number of deaths in winter

months (November–February) than in the summer months (June–August)” (the met-office definition of

winter which we use in this paper, December to February, covers a narrower period than mentioned by

London).

The London paper analysed fire deaths between 1996 and 2000, well before the introduction of Integrated

Risk Management Planning and the provision of home fire safety visits for householders, so it is possible

that the study reflected the reality of the time and not what would be found now.

A more recent study from 2014 in the Wirral in Merseyside3 found that “Fire fatalities followed a seasonal

trend, with the highest number of fatalities occurring in the winter months, peaking in January”. The Wirral

is a much smaller area with far lower population and far fewer dwelling fires each year than for Scotland as

a whole, and with known deprivation issues. The figures quoted in the study are thus not directly

comparable to our own situation.

2 Holborn, P. G., P. F. Nolan, and J. Golt. "An analysis of fatal unintentional dwelling fires investigated by London Fire

Brigade between 1996 and 2000." Fire Safety Journal 38.1 (2003): 1-42. 3 Donaldson, Anna. "ACCIDENTAL DWELLING FIRES IN WIRRAL." (2014).

19 July 2016

14 | P a g e

Appendix 1: Tabulated Statistics

Table 1: Statistics for Accidental Dwelling Fires by Month

Fiscal Month

Overall Mean

Overall Median Min

Lower Quartile Mean Median

Upper Quartile Max t test

t test %

01-Apr 422 418 378 396 419 420 438 467 0.792 79.2

02-May 422 418 393 418 423 422 428 454 0.889 88.9

03-Jun 422 418 383 389 393 393 397 401 0.000 0.0

04-Jul 422 418 343 374 403 394 433 467 0.301 30.1

05-Aug 422 418 358 382 397 392 417 432 0.049 4.9

06-Sep 422 418 379 394 399 400 405 417 0.002 0.2

07-Oct 422 418 365 407 415 423 429 448 0.543 54.3

08-Nov 422 418 364 414 427 436 444 475 0.711 71.1

09-Dec 422 418 451 469 498 488 520 570 0.003 0.3

10-Jan 422 418 358 418 448 439 486 530 0.282 28.2

11-Feb 422 418 317 394 407 415 432 463 0.428 42.8

12-Mar 422 418 374 420 430 432 448 467 0.516 51.6

Table 2: Statistics for Deliberate Dwelling Fires by Month

Fiscal Month

Overall Mean

Overall Median Min

Lower Quartile Mean Median

Upper Quartile Max t test

t test %

01-Apr 72 66 49 58 74 71 78 125 0.864 86.4

02-May 72 66 50 52 78 87 97 114 0.557 55.7

03-Jun 72 66 50 58 75 72 88 109 0.749 74.9

04-Jul 72 66 44 62 79 80 96 114 0.485 48.5

05-Aug 72 66 39 49 69 63 90 105 0.803 80.3

06-Sep 72 66 38 58 67 66 79 94 0.549 54.9

07-Oct 72 66 48 57 73 67 88 106 0.919 91.9

08-Nov 72 66 56 64 86 75 106 133 0.251 25.1

09-Dec 72 66 47 59 70 61 80 101 0.745 74.5

10-Jan 72 66 46 52 63 63 72 88 0.187 18.7

11-Feb 72 66 26 43 58 53 77 85 0.143 14.3

12-Mar 72 66 40 50 68 72 84 94 0.608 60.8

19 July 2016

15 | P a g e

Table 3: Statistics for Accidental Dwelling Fire Fatalities by Month

Fiscal Month

Overall Mean

Overall Median Min

Lower Quartile Mean Median

Upper Quartile Max t test

t test %

01-Apr 3 3 1 2 3 3 4 5 0.805 80.5

02-May 3 3 2 2 3 3 3 4 0.604 60.4

03-Jun 3 3 1 2 3 2 3 6 0.534 53.4

04-Jul 3 3 0 1 3 2 4 7 0.793 79.3

05-Aug 3 3 0 2 2 2 3 4 0.172 17.2

06-Sep 3 3 1 1 2 2 2 3 0.004 0.4

07-Oct 3 3 0 0 2 4 4 4 0.476 47.6

08-Nov 3 3 1 3 4 4 4 6 0.310 31.0

09-Dec 3 3 2 3 4 3 5 6 0.172 17.2

10-Jan 3 3 1 2 4 4 4 12 0.334 33.4

11-Feb 3 3 0 3 4 4 4 7 0.411 41.1

12-Mar 3 3 0 4 4 5 5 7 0.244 24.4

Table 4: Statistics for Accidental Dwelling Fire Fatalities Per Thousand Incidents by Month

Fiscal Month

Overall Mean

Overall Median Min

Lower Quartile Mean Median

Upper Quartile Max t test

t test %

01-Apr 7 7 3 5 7 7 8 11 0.768 76.8

02-May 7 7 5 6 7 7 7 10 0.774 77.4

03-Jun 7 7 3 4 7 5 8 15 0.787 78.7

04-Jul 7 7 0 2 6 5 9 15 0.732 73.2

05-Aug 7 7 0 4 5 5 7 11 0.280 28.0

06-Sep 7 7 2 3 4 5 5 7 0.009 0.9

07-Oct 7 7 0 1 6 9 9 9 0.473 47.3

08-Nov 7 7 2 7 9 9 11 15 0.309 30.9

09-Dec 7 7 4 6 8 6 10 12 0.515 51.5

10-Jan 7 7 3 5 10 8 10 27 0.400 40.0

11-Feb 7 7 0 7 9 10 10 16 0.374 37.4

12-Mar 7 7 0 8 10 11 12 16 0.250 25.0

19 July 2016

16 | P a g e

Appendix 2: List of Charts and Tables

Charts

Figure 1: Monthly totals for accidental dwelling fires ....................................................................................... 3

Figure 2: Accidental dwelling fire seasonal decomposition .............................................................................. 3

Figure 3: Monthly totals for deliberate dwelling fires ....................................................................................... 4

Figure 4: Deliberate dwelling fire seasonal decomposition .............................................................................. 4

Figure 5: Accidental dwelling fires Heat-map .................................................................................................... 5

Figure 6: Deliberate dwelling fires Heat-map.................................................................................................... 5

Figure 7: Accidental dwelling fires boxplot ....................................................................................................... 6

Figure 8: Seasonal boxplot of accidental dwelling fire totals ............................................................................ 7

Figure 9: Deliberate dwelling fires boxplot ....................................................................................................... 8

Figure 10: Seasonal boxplot for deliberate dwelling fires ................................................................................. 8

Figure 11: Differences between annual monthly mean and individual monthly totals for deliberate dwelling

fires .................................................................................................................................................................... 9

Figure 12: Accidental dwelling fire fatalities by month ................................................................................... 10

Figure 13: Seasonal decomposition of accidental dwelling fire fatalities per thousand incidents ................. 10

Figure 14: Accidental dwelling fire fatalities boxplot ...................................................................................... 11

Figure 15: Normalised fire fatality rates per month ........................................................................................ 11

Figure 16: Seasonal accidental dwelling fire fatalities per thousand incidents .............................................. 12

Tables

Table 1: Statistics for Accidental Dwelling Fires by Month ............................................................................. 14

Table 2: Statistics for Deliberate Dwelling Fires by Month ............................................................................. 14

Table 3: Statistics for Accidental Dwelling Fire Fatalities by Month ............................................................... 15

Table 4: Statistics for Accidental Dwelling Fire Fatalities Per Thousand Incidents by Month......................... 15